The present invention relates to the field of fuel injection pumps in which one or more cam-actuated transfer pumps is arranged to supply fuel to fuel injectors of an associated internal combustion engine. More particularly, the invention relates to mechanisms for varying the timing of fuel delivery by such pumps and, most particularly, to a mechanism for externally setting an initial position of a piston in such a pump timing mechanism to thereby set a datum timing position of the pump with respect to the rotary phase of the engine.
In U.S. Pat. No. 6,041,759, the relevant disclosure of which is incorporated herein by reference, there is provided a mechanism for advancing and retarding fuel injection comprising an advance piston slidable within a bore, the advance piston cooperating, in use, with an actuating lever of a cam arrangement of a fuel pump to adjust the timing of fuel delivery by the pump; a servo-piston slidable in a bore provided in the advance piston; a light load piston moveable relative to the advance piston against the action of a light load control spring; a servo-control spring engaged between the light load piston and the servo-piston; a light load control valve operable to control the application of fuel to the light load piston to adjust timing under light load conditions; and an independent temperature control valve operable to control the application of fuel to the light load piston depending upon the engine temperature to permit adjustment of the timing of fuel delivery to compensate for cold conditions. The apparatus is substantially as disclosed in the present FIG. 1 which corresponds to FIG. 2 in the incorporated reference.
A prior art mechanism associated with the fuel injection pump can adjust the timing of fuel injection in accordance with, among other things, operating load and speed of the associated internal combustion engine. However, the initial datum or reference timing position of the arrangement, in relation to which adjustments by the advance mechanism takes place, is achieved by physically securing the pump to the associated engine in an empirically-determined angular orientation in relation to the pump drive mechanism. Subsequent adjustment of the datum position is particularly inconvenient, and may be extremely difficult and time-consuming, in that the engine must be run and then stopped to permit datum adjustment by loosening and further changing the angular orientation of the pump. In many installations, access to the pump mounting flange is significantly restricted.
It is a principal object of the invention to provide an improved advance mechanism for a fuel injection pump wherein the datum position of the mechanism may be adjusted externally of the mechanism without requiring rotational repositioning of the pump.
It is a further object of this invention to provide an improved advance mechanism for a fuel injection pump wherein a servo-piston can function as an element of a light load piston assembly in response to variations in engine load and can also function independently of a light load piston in response to variations in engine speed to control the position of the advance piston and hence the timing of the associated fuel injector, the datum position of the advance piston being adjustable externally of the mechanism without requiring rotational repositioning of the pump.
Briefly described, the present invention is directed to an improved mechanism for advancing and retarding the injection timing of a mechanically-actuated fuel injection pump. The mechanism includes a housing having a bore slidably receivable of an advance piston which cooperates with a lever of the fuel injecting mechanism to adjust the injection timing of a fuel injection pump. A light load piston also in the bore cooperates with the advance piston to permit adjustment of timing under light load conditions. A rotatable cam mechanism cooperates with a flange on the light-load piston to set the axial rest position of the light-load piston, and hence of the advance piston, and hence to set the datum timing of the fuel injection pump. The cam may be easily rotated by external adjustment of the mechanism.
In a preferred embodiment, a servo-piston is slidable in a bore provided in the advance piston; the light load piston is moveable relative to the advance piston against the action of a light load control spring; a servo control spring is engaged between the light load piston and the servo-piston; a light load control valve is operable to control the application of fuel to the light load piston to adjust timing under light load conditions; and an independent temperature control valve is operable to control the application of fuel to the light load piston depending upon the engine temperature to permit adjustment of the timing of fuel delivery to compensate for cold conditions.